Pressure sensing devices are commonly used in a variety manufacturing and chemical processes. As discussed in U.S. Pat. No. 5,852,244, it is necessary in the manufacture of semi-conductor wafers to employ sensing devices which do not leak and contaminate the semiconductor wafers being produced. The highly corrosive fluids used in the manufacture of semi-conductive wafers flow through a passageway either made from or lined with an inert material, such as, for example a fluorocarbon polymer such a Teflon(copyright). In the device disclosed in U.S. Pat. No. 5,852,244, a bore extends through and into the passageway and an isolation member is placed in this bore. Seals are employed to prevent leakage, but these seals may not be effective or deteriorate over prolonged periods. Consequently, it is highly desirable to provide a sensor which eliminates or minimizes the possibility of leakage.
In accordance with this invention, leakage is eliminated or minimized using redundant or dual barriers made of a chemically inert material instead of an isolation member mounted by seals in an opening next to the sensor. The chemically inert material is not reactive with highly corrosive fluids that have extreme pH levees either, highly acidic or basic.
This invention has several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims that follow, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled, xe2x80x9cDETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS,xe2x80x9d one will understand how the features of this invention provide its benefits, which include, but are not limited to:
(a) redundant safety barriers to corrosive fluids,
(b) ease of manufacture, assembly, and installation,
(c) ease of temperature sensor integration,
(d) no externally exposed metallic surfaces, and
(e) lower maintenance,
The first feature of the pressure sensing device of this invention is that it is adapted to measure the pressure of a corrosive fluid and includes a dual containment system. The device includes a chamber and uses a pressure sensor adjacent the chamber that provides a signal proportionate to the pressure of the fluid within the chamber. The chamber has (1) an inlet into which the fluid is introduced and an internal surface in contact with the fluid that is made of a material that does not react with the fluid and (2) a thin wall in contact with the sensor which is mounted outside to the chamber and next to the thin wall. The thin wall is less than about 0.05 inch, and preferably has a thickness of from about 0.005 to about 0.05 inch. This thin wall, being integral with the body of the chamber, acts as a secondary fluid containment barrier. There is primary containment barrier within the chamber made of a material that does not react with the fluid. This primary containment barrier comprises a liner that bears against the internal surfaces of the chamber. The liner is nested snugly within the chamber. The primary containment barrier may include a chemically inert plug having a chemically inert temperature probe therein.
The second feature is that the primary containment also has a thin wall that abuts and is contiguous with the thin wall of the chamber. The secondary and primary containment barriers have mating surfaces, and the sensor and thin wall of the chamber have mating surfaces. All these mating surfaces are in vacuum contact. Preferably, the mating surfaces form interference fit seals. For example, the interference fit seals may comprise tongue and groove components.
The third feature is that at the sensor has an interior surface with a predetermined profile, and the thin wall has a predetermined profile that is substantially the same as the predetermined profile of the interior surface of the sensor. Preferably, the predetermined profile of the interior surface of the sensor includes an annular groove and the predetermined profile of the thin wall includes an annular raised portion that fits snug within the annular groove in the interior surface of the sensor device. The thin wall diaphragm section having an exterior surface of a shape that conforms to the interior surface of the first thin wall diaphragm section and abuts and covers substantially the entire interior surface of the first thin wall diaphragm.
The forth feature is that the device includes a clamping mechanism that applies a uniformly distributed tie down load on the sensor. The clamping mechanism includes metallic elements that are enclosed with a chemically inert housing. This clamping mechanism includes a header member that overlies the sensor device and has a n interior surface that bears against the exterior surface of the sensor device, said interior surface of the header member and the exterior surface of the sensor device having elements therein that mate with each other. The interior surface of the header member has an outer edge with an outward extending rim and the sensor device has a disk shape with an upper outer edge that has a step therein. The rim i s seated on the step.
This invention also includes a sensor. This sensor includes a disk shaped support member having an exterior surface and an interior surface. The interior surface has a mating element adapted to interlock with a counterpart mating element on another structure. The exterior surface has with a bridge resistor circuit mounted thereon. The mating element comprises an annular grove that encompasses the bridge resistor circuit. The bridge resistor circuit provides a signal proportionate to the pressure of the fluid within chamber. Because the sensor is mounted to the exterior of the body member adjacent the thin wall, the sensor changes shape as the thin wall changes shape in response to changes in the pressure of the fluid within the chamber.